摘要:

The photoisomerization of a series of protonated, methyl substituted phenols to protonated bicyclo[3.1.0]hexenones has been examined. These reactions, which were carried out in CF3SO3H as a strong acid solvent at ambient temperatures, provide a convenient route to a variety of bicyclo[3.1.0]hexenones. The quantum yields for these photoisomerizations vary from 0.018 for protonated 3,5-dimethylphenol to 0.65 for protonated 2,6-dimethylphenol. This variation in efficiency can be understood in terms of a competition between ring opening, to regenerate the starting phenol, or cyclopropyl migration, to give product, of an initially formed intermediate.

ISSN:0008-4042    

DOI:10.1139/v88-217

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The thermal isomerization of a wide range of protonated methyl substituted bicyclo[3.1.0]hex-3-en-2-ones to protonated phenols has been examined using triflic acid as a strong acid solvent. The rate constants and activation energies of these isomerizations have been determined. The barriers to the isomerizations were shown to be dependent on the number and position of the methyl substituents. The results show that three different mechanisms are needed to account for these isomerizations, two of which involve a preliminary circumambulatory rearrangement prior to ring opening and the other process involving a direct ring opening of the initial protonated bicyclohexenone to give an intermediatemeta-protonated phenol.

ISSN:0008-4042    

DOI:10.1139/v88-218

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The conformations of several protonated enones have been determined by low temperature13C nuclear magnetic resonance spectroscopy. Information on the ground state conformation has been used to understand the differences in the photochemistry of these systems. Photoisomerizations of4and5have been examined. In the case of4, irradiation leads only to the formation of theZisomer16; protonated dihydrofuran13was not observed. In the case of5, both theZisomer17and protonated dihydrofuran14were observed. The protonated dihydrofuran14was produced from the start of the reaction. It is concluded from these and previous results that for the photocyclization to occur the starting cation must exist in ans-cisconformation in the ground state.

ISSN:0008-4042    

DOI:10.1139/v88-219

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The anions of dithioacetals react with epoxides to give β-hydroxydithioketals, which can be oxidized and hydrolyzed to β-diketones. This sequence is applied to a model study of the synthesis of the C-5 to C-15 fragment of the antibiotic ionomycin.

ISSN:0008-4042    

DOI:10.1139/v88-220

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Ultraviolet initiated liquid phase oxidation of neattrans-1,2-dichloroethene (1a) with oxygen at 30 °C afforded ca. 45% of the combined Cl-products CO, CO2, and phosgene as well as nine oxygenated and nine non-oxygenated chlorinated organic products. Major oxygenated products werecis- andtrans-2,3-dichlorooxirane (6a,b) and 1,2,2-trichloroethyl formate (13); minor products were e.g.,mesoandracbis(1,2,2-trichloroethyl) ether (11c,d) and dichloromethyl 1,2,2-trichloroethyl ether (12). The mode of formation of all products is rationalized by a unified reaction scheme.

ISSN:0008-4042    

DOI:10.1139/v88-221

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The adsorption behaviour of benzene (A), toluene (A),p-xylene (A), ando-xylene (A) in their binary mixtures witho-chlorotoluene (B) on silica gel has been studied at 308.15 K. The data have been analysed in terms of a model that assumes that partition and surface reactions play an important role in the adsorption process, and have revealed that while both partition and surface reactions dictate the adsorption (U-shaped isotherms) ofo-chlorotoluene (OCTE) (B) from benzene (A) or toluene (A) + OCTE (B) mixtures, the adsorption of A and B entities ofp-xylene (A) oro-xylene (A) + OCTE (B) mixtures (S-shaped isotherms) onto the silica gel surface is governed primarily by the distribution process and secondarily by the surface reaction.

ISSN:0008-4042    

DOI:10.1139/v88-222

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The CH3Hg+cation forms a zwitterionic complex CH3Hg[HOCH2CH(NH2)CO2—N,O,O] with serine in aqueous solution. X-ray diffraction (P212121,a = 5.821,b = 8.052,c = 14.307 Å,R = 0.021) shows that mercury is linearly bonded to the NH2end of the amino acid, whereas one carboxylate oxygen and the side-chain hydroxyl group establish secondary Hg—O bonds. Coordination leads to characteristic changes in the infrared and Raman spectra of serine. From the1H and13C nmr spectra, N-coordination is found to be retained in aqueous solution, whereas the ligand conformation observed in the solid accounts for 76% of the conformer distribution.

ISSN:0008-4042    

DOI:10.1139/v88-223

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The cycloaddition of nitrilimines1a–eto ethyl α-cyanocinnamate6afurnished the 2-pyrazoline derivatives11a–erespectively. Similar reactions of1a–ewith ethyl α-cyano-p-nitrocinnamate6byielded 1,3-disubstituted 4-(p-nitrophenyl)-5-ethoxycarbonylpyrazoles14a–e, via elimination of hydrogen cyanide from their precursors, the 2-pyrazoline derivatives13a–e, respectively. The structures of the cycloadducts11and14were supported by spectral (13C and1H nuclear magnetic resonance and infrared) and analytical data.

ISSN:0008-4042    

DOI:10.1139/v88-224

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The preparation of 6α-methyl-2-methyl-6β-phenoxyacetamidopenem-3-carboxylate, 6α-methoxy-2-methyl-6β-phenoxyacetamidopenem-3-carboxylate, and 6α-methoxy-2-methyl-6β-phenylmalonylamidopenem-3-carboxylate from penicillin V and 6-aminopenicillanic acid is described. These penems have been isolated and characterized as their sodium or potassium salt. The chemical stability of the above compounds was determined as their half-life in aqueous buffer. In this way, it was found that the 6α-methyl analog was more stable than the parent 6-monosubstituted acylaminopenem while the remaining analogs were of comparable stability.

ISSN:0008-4042    

DOI:10.1139/v88-225

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A chiral intermediate bearing the 1-β-methyl moiety (14a) for 1-β-methylcarbapenem antibiotics (1) was prepared by stereoselective aldol-type reaction between 4-acetoxyazetidinone3aand the dianion (or corresponding bissilyl enol ether) of a 3-oxopentanoate12or13in the presence of a metal salt. A major side reaction has also been elucidated.

ISSN:0008-4042    

DOI:10.1139/v88-226

出版商:NRC Research Press    

年代:1988

数据来源: NRC